Fvwm

"Fvwm was created by Robert Nation. It is based on code from 'twm' (Tom's Window Manager) which was at the time perhaps the only real window manager available. Frustrated with the lack of features and the fact that 'twm' was full of memory leaks, Rob began hacking on it; the result was that Fvwm was kick-started in early 1993. Rob had, in fact, already made a name for himself as the author of the popular terminal emulator rxvt, which is still used by a lot of people today."Story